The invention relates to injection needles mounted in needle hubs, the needles having an injection part with a skin piercing obliquely cut end and being fastened in the needle hub for mounting on a syringe.
Such needles are often shaped as double pointed needles in which each needle, in addition to a skin piercing point, has at the other end of the needle a point which pierces a rubber membrane which closes an ampoule containing the liquid to be injected.
Needles of the above kind are used for injection of liquids, e.g. insulin, which have to be injected subcoutaneously. i.e. in the subcutis lying between the cutis and a muscle membrane which cover the underlying muscles. If insulin is injected into the muscle it will be absorbed in the body too quickly and an unwanted drop in the blood sugar level may be the result. On the other hand insulin injected in the cutis will not be absorbed at all or in an unpredictable way.
To be sure that intramuscular injection is avoided an injection technique may be used by which the skin is gripped by one hand between the thumb and the side of the index finger so that a fold of the skin is formed and thereafter the needle insertion and the injection are performed with the injection device held in the other hand. The technique described makes the injection a two hand operation, and even a third hand could be useful for drawing and keeping away clothes normally covering the injection zone.
It is an object of the invention to provide a needle suited for use by subcoutaneous injections which needle may mainly be inserted without making it necessary to form a fold of the skin and by which the injection consequently occupies only one hand. Allthough the injection of insulin is described as an example, the needle is useful for all kinds of subcoutaneus injections, e.g. for injecton of growth hormone.
EP 279 583 mentions the provision of needles the injection part of which has an overall length of 8-12 mm. This length will seen in relation to the often used 16 mm needles reduce the risk for performing intramuscular injections, but by slim males the sum of the thicknesses of the cutis and the subcutis may even be smaller than 8 mm and the risk for intramuscular injection will still be unacceptable.
From EP 279 583 it is known to reduce the effective length of a 12.5 mm long needle by mounting on the needle hub a skirt surrounding the needle coaxially in a distance from said needle. The skirt only leaves a minor length of the needle free for injection. Skirts of different lengths may be used to leave 4 or 8 mm of the needle free for penetration of the skin. The effective length of the needle is only well defined by insertion perpendicular to the skin whereas the effective length is further reduced in a not well defined way if the needle is inserted at an oblique angle.
Needles having lengths between 3 mm and 4 mm have been discussed but being that short a needle will hardly be able to penetrate the cutis, especially not when the needle is inserted at an oblique angle.
The risk of making intramuscular injections or injections in cutis is heavily reduced when a needle is used by which according to the invention the overall length of the injection part of the needle extending from its fastening in the needle hub to its skin piercing end lies in the interval 4-6 mm.
The shorter overall length of the injection part of the needle counted from its support in the hub to the skin piercing point enables use of thin and thin walled needles with reduced risk for cracking. This reduced risk is not obtained by needles the effective length of which are reduced by surrounding a part of the needle with a sleeve which does not support the needle.
As it is possible to administer insulin through needles as thin as G30, administration will also be possible through a thin walled needle having a bore larger than 0.133 mm which corresponds to the smallest bore of a G30 needle. If the outer diameter is set as the largest diameter allowed for a G30 needle, thin walls will allow a larger bore than known from a normal G30 needle.
According to an embodiment of the invention the outer diameter of the needle and the diameter of the bore of the needle may comply with one of the following conditions:
a) the outer diameter is smaller than 0.320 mm and the diameter of the bore is larger than 0.165 mm, or
b) the outer diameter is smaller than 0.298 mm and the diameter of the bore is larger than 0.133 mm.
In the following the invention is described in more details with reference to the drawing.